The study was conducted across wild, urban and rural areas, highlighting the widespread nature of antibiotic resistance.
Antimicrobial resistance (AMR) has been a growing problem for a number of years now, with resistance against antimicrobials key for human medicine being especially worrying.
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However, new research has found that wildlife such as foxes and birds could be critical early warning systems for antibiotic resistance at the ecosystem level.
The study, which was first published in the Frontiers of Microbiology journal, evaluates the presence of enzyme-encoding genes in wildlife faecal samples, which can prove resistance to essential antibiotics like third-generation cephalosporins (3GCs), used to treat sepsis, pneumonia and meningitis.
These genes can spread through bacterial groups like ESKAPE, which are particularly resistant and can often sidestep antibacterial agents. One ESKAPE group bacterium, Klebsiella pneumoniae, has even spread much beyond systems and places directly exposed to antibiotics and can cause severe infections in humans.
“We isolated a high-risk ST307 clone of K pneumoniae and NDM-5 carbapenemase, an enzyme variant that can inactivate antibiotics, from wildlife living far from human activity,” Dr Mauro Conter, an associate professor at the Department of Veterinary Medical Sciences at the University of Parma, said.
“This confirms the role of wildlife as reservoirs of clinically relevant resistance, which means that wildlife surveillance could provide an early warning system of resistance spreading beyond clinical settings.”
Birds and foxes provide warning signs of antibiotic resistance
The study included almost 500 faecal samples from crows, magpies, red foxes and several species of water birds.
These were taken while animals were moving as usual through rural, urban and wild areas, collecting AMR across regions and ecosystems without having received antibiotics themselves. They were tested for Klebsiella spp, a bacterial genus that includes K pneumoniae and other highly dangerous pathogens.
Klebsiella spp in particular produce carbapenemases, which can render last-resort antibiotics used to treat severe infections caused by multidrug-resistant bacteria useless.
The results showed that birds are primarily responsible for dispersing resistance by air over long distances, whereas foxes contribute most to short-range AMR dissemination on land.
Klebsiella spp was present in 32 samples, while K pneumoniae was in 2% of samples, mainly in foxes and waterbirds.
“Even a 2% prevalence in wildlife represents environmental contamination by high-risk clones. K pneumoniae readily spills over through water and waste routes, creating a continuous human-animal-environment resistance cycle,” Conter noted.
Compared to 2024 data, K pneumoniae isolates in this research also had higher resistance to almost all antibiotic classes.
“Our study showed that wildlife resistance exceeds clinical rates,” explained Conter.
“100% of K pneumoniae isolates from wildlife in our study were resistant to 3GCs. Compared to this, only 19.6% of K pneumoniae isolates from human patients in Italy were resistant to 3GCs, according to the latest European Centre for Disease Prevention and Control surveillance data.”
How to fight antibiotic resistance at ecosystem levels
To curb the growing trend of AMR bacteria across wildlife and ecosystems not directly exposed to antibiotics, companies and governments alike need to take active steps to reduce antibiotic pollution in wastewater.
Similarly, sewage treatment needs to be enhanced, while antimicrobials in livestock should be used more cautiously to limit the use of key antibiotics in human medicine.
However, the study still has limitations regarding transmission links between wildlife and humans and the prevalence of resistance.
Larger studies could highlight the real diversity of bacteria present in wildlife. However, they can be expensive and challenging to implement.
“What we see is a complex problem that requires ‘one health’ solutions addressing antibiotic pollution, climate-driven wildlife behavioral changes, and bacterial population dynamics,” Conter noted.
“Our data justify routine wildlife AMR monitoring as a public health early warning system, guiding environmental interventions before resistance reaches clinical settings.”
